ABSTRACT
<p><b>OBJECTIVE</b>To study the role of lateral collateral ligament complex on the posterolateral rotatory instability and the relationship between the radiocapitellar ratio (RCR) and the injury of lateral collateral ligament complex on X-ray images.</p><p><b>METHODS</b>Twenty elbow joints from fresh-frozen adult cadavers were used to make osteo-ligamentous elbow specimens. The specimens were fixed with a self-made device to maintain posterolateral rotatory instability of the elbow joint. All the specimens were divided into two groups: group A and group B. Surgical procedures were carried out as follows in the lateral structures of group A: A1, intact specimen; A2, transection of radial ulnar collateral ligament firstly; A3, transection of annular ligament secondly; A4, final transection of the radial collateral ligament. The procedures in group B were carried out as follows: B1, intact specimen; B2, transection of the radial collateral ligament firstly; B3, transection of the annular ligament secondly; B4, final transection of the radial ulnar collateral ligament. Lateral X-ray films of elbow joint were taken, and the radiocapitellar ratio (RCR) was measured by using PACS. All analysis was performed with SPSS 17.0 software.</p><p><b>RESULTS</b>Group A: the increases in RCR had statistical differences among A1, A2, A3, and A4 groups. Group B: the increases in RCR had no statistical differences among B1, B2 and B3 groups; but the increase in RCR in group B4 was more than that in B1, B2 and B3 groups.</p><p><b>CONCLUSION</b>The radial ulnar collateral ligament is a key structure to maintain posterolateral rotatory stability;the radial collateral ligament and the annular ligament are the secondary important structures. There are 4 grades of the posterolateral rotatory instability of the elbow, according to the X-ray imaging classification.</p>